Right On Time Distributed Shared Memory

The demand for real-time data storage in distributed control systems (DCSs) is growing. Yet, providing real- time DCS guarantees is challenging, especially when more and more sensor and actuator devices are connected to industrial plants and message loss needs to be taken into account. In this paper, we investigate how to build a shared memory abstraction for DCSs as a first step towards implementing different shared storage systems in a DCS context. We first prove that, in the presence of host crashes and message losses, the necessary guarantees of such an abstraction are impossible to implement using a traditional approach that has no access to the internals of existing DCS services, e.g., a modular approach where algorithms are built on top of existing software blocks like failure detectors. We propose a white-box approach that utilizes messages of existing services in any DCS as the sole means of communication. More precisely, we present TapeWorm, an algorithm that attaches itself to the heartbeat messages of the failure detector component in DCSs. We prove that TapeWorm implements the desired shared memory guarantees for applications running on a DCS. We also analyze the performance of TapeWorm and we showcase ways of adapting TapeWorm to various application needs and workloads

Implementation of a Flexible Membership Protocol on a Real-Time Ethernet Prototype

This paper describes the implementation of a processorgroup membership protocol in an experimental real-time network. The protocol is appropriate for fault-tolerant distributed systems using TDMA for scheduling messages. It allows nodes to maintain a consensus on the operational state of all nodes, in the presence of node failures and restarts, as well as network failures. The protocol is based on the principle that, in a system of n nodes, each node must acknowledge the messages from k other nodes in the membership group, where k can assume values between 2 and n 1. Membership agreement is guaranteed if f k 1 failures occur during n consecutive transmission slots. We have implemented the membership protocol in a time-triggered network based on COTS Ethernet hardware, programmed to schedule messages according to the TDMA method

Implementation of a Flexible Membership Protocol on a Real-Time Ethernet Prototype

This paper describes the implementation of a processorgroup membership protocol in an experimental real-time network. The protocol is appropriate for fault-tolerant distributed systems using TDMA for scheduling messages. It allows nodes to maintain a consensus on the operational state of all nodes, in the presence of node failures and restarts, as well as network failures. The protocol is based on the principle that, in a system of n nodes, each node must acknowledge the messages from k other nodes in the membership group, where k can assume values between 2 and n 1. Membership agreement is guaranteed if f k 1 failures occur during n consecutive transmission slots. We have implemented the membership protocol in a time-triggered network based on COTS Ethernet hardware, programmed to schedule messages according to the TDMA method